A supplier
of nano-positioning systems for Atomic Force Microscopy (AFM)
is using non-contact capacitive displacement sensors from Micro-Epsilon
to measure the travel distance of test items down to nanometre
resolution. The sensors also have to operate in extreme conditions,
with ambient temperatures of -270 degrees Centigrade and in an
ultra-high vacuum.

Based in Munich,
attocube systems AG specialises in the development, manufacture
and distribution of innovative nano-positioning systems. Founded
in 2001, the company is a spin-off from the CeNS Munich (Center
for NanoScience) in Germany. The company's core competence is
in ultra-high precision spatial positioning of objects - a prerequisite
for most nanotechnology applications. attocube's unique technology
enables the positioning and scanning of objects with atomic resolution,
but with travel distances in the centimetre range.

attocube has
developed systems for a variety of extreme environments, including
UHV applications, low temperatures and high magnetic fields.
These systems have enabled pioneering investigations in science
and industry, opening up new markets in semiconductors, biotechnology,
material science, medicine, chemistry and aerospace.

Atomic force
microscopes are used to image, measure and manipulate matter
at the nanoscale. The information is gathered by 'feeling' the
surface with a mechanical probe. Piezoelectric elements that
facilitate very small but accurate and precise movements on command
enable very precise scanning of surfaces.

attocube is using
two custom-designed capaNCDT 6300 CSH1FL capacitive displacement
sensors from Micro-Epsilon to measure the travel displacement
of test items that need to be moved in the nanometre range, enabling
surface topography data to be obtained. Attocube has developed
special actuator motors that are used to position the head of
the microscope for these precise positioning tasks.

The system uses
a piezo-ceramic positioning unit, enabling movement of the x-,
y- and z-axis. The two sensors measure the positioning range,
which is 1.2mm by 1.2mm. The complete head of the microscope
is cooled using liquid helium to 4K above the absolute zero point
of -273 degrees Centigrade. The traversing units operate at an
ambient temperature of 4K in an ultra-high vacuum and under very
strong magnetic fields.

In order to measure
the x- and y-axis movements, attocube has integrated two Micro-Epsilon
capaNCDT 6300 sensors with its actuator motors, positioned inside
the head of the microscope. With a measuring range of 1mm, the
sensors have a precision of less than 5nm and operate without
contact.

Chris Jones,
Managing Director at Micro-Epsilon (UK) Ltd comments: "The
extremely low ambient temperature and ultra-high vacuum were
particular challenges here. In ultra-high vacuums, you tend to
get degassing of sensor materials and components, both within
the sensor itself and the cable. The solution had to operate
without contamination in this environment and also experience
no loss in signal quality when passing sensor signals through
an ultra-high vacuum bulkhead connector."

Because the sensors
are expected to perform just as well at -269 degrees Centigrade
as they are at room temperature, Micro-Epsilon therefore used
special materials for the sensor and the cable, which due to
their very low thermal expansion properties, provide very stable
sensor measurements. A complete sensor solution with vacuum bulkhead
was delivered to the customer that required no modifications.
The cable supplied is a triaxial design and the temperature stability
of the complete system is 11ppm/degrees Centigrade (most alternative
sensors offer 100-200ppm at best).

Jones continues:
"We also had a very tight space envelope to work in and
so we had to modify the sensor geometry to suit the installation.
We also developed our own in-house low temperature test chamber
that enables us to calibrate and test our sensors for these types
of extreme application down to -200 degrees Centigrade."

The capaNCDT
6300 CSH1FL is now part of the standard Micro-Epsilon range of
capacitive displacement sensors._________________________________________________________